Molecular Organization of Glycosphingolipids in Phosphatidylcholine Bilayers and Biological Membranes

Abstract

Glycosphingolipids, in contrast to glycerol-based lipids, are relatively minor components of mammalian cell membranes. They are, however, confined to the external surface of the plasma membrane and in this surface may collectively be a major component (1–4). In some cell types very small amounts of these lipids have been found associated with Golgi membranes, their probable site of biosynthesis (1). Their location on the trans-cytoplasmic side of the plasma membrane causes them, together with glycosylated membrane proteins, to be the primary components of the cell to interact with the molecules and other cells of the immediate environment. Thus specific glycosphingolipids have been shown to serve as receptors for toxins, viruses and some hormones (2,5–11). They have long been known to act as antigenic determinants and to mediate immune responses (11–13). There is much evidence to suggest that glycosphingolipids play a role in cell-cell interaction and recognition (7). Alterations in the amounts and types of these lipids on the cell surface are very often associated with growth, differentiation, development, aging (7,14,15), and with oncogenic transformation (11,16). Although there is considerable information about the molecular structure of many glycosphingolipids, relatively little is known about the organization of molecules of this class in phospholipid bilayers and in the bilayers of biological membranes. It seems certain that their molecular organization is a critical parameter underlying many of the functions of glycosphingolipids (17).